Steve Hagar wrote:
> So far all of the antenna guides I have seen note the
> installation of the ferrite "baluns" on the antenna lead
> going to the dipole. This to reduce the reflected power going
> down the lead. I am getting ready to stuff an Archer
> antenna up in the tailfin before bonding the top and bottom
> halfs together. The instructions for the Archer do no detail
> the installation of the toriods. Since this installation is
> inaccessable once everything is together I was going to
> install these items on the cable anyway. The queston is has
> any one had to do this to reduce reeflected power on the
> Archer? In addition, is having the toroids on the cable in
> any way detrimental to the performance of the antenna if
> there is not a reflected power issue?
Putting toroids on the cable is never detrimental to the performance of
the antenna. In a few cases, they will make no difference at all, such
as with ground plane antennas mounted on metal airplanes. Their effect
on the radiation pattern is typically not large, but the net effect
should virtually always be beneficial, especially in the case of a
vertical antenna fed by a horizontal run of coax.
Of greater importance to us are the other effects of current flowing on
the outside of the coax shield, which is what the toroids suppress.
This current can couple into nearby wires and electronic devices,
increasing the potential for interference from the radio transmitter. I
would rather keep the radiation confined as much as possible to the
antenna in the tail, rather than allowing it along the length of the
feedline.
Current on the outside of the shield can also affect the reading of an
swr meter, making it more difficult to find the dip that occurs when the
antenna is trimmed to the resonant length. For me, there is no doubt
that the benefits of the toroids are well worth the dollar cost and few
grams of weight.
Dave DeFord
N135TD
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